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V <br /> 1590 Solano Way <br /> #A <br /> Concord, CA 94520 <br /> 925.688.1200 PHONE <br /> 925.688.0388 Fax E C-'EtI��/ �� U <br /> www.TRCsolutions.com MAR 1. 8 2009 <br /> March 13, 2009 ENVIRONMEN i 'iEALTN project No. 164690 <br /> PERMIT/SERVICES <br /> Ms. Lori Duncan <br /> San Joaquin County <br /> Environmental Health Department <br /> 600 East Main Street <br /> Stockton,California 95202 <br /> SITE: Central California Traction Company(CCT)Stockton Railyard <br /> 1645 Cherokee Road <br /> Stockton, California <br /> RE: Response to SJCEHD Comments on the Quarterly Monitoring Report— <br /> Fourth Quarter 2oo8 <br /> Dear Ms. Duncan: <br /> On behalf of Central California Traction Company (CCT), TRC is responding to your <br /> March 2, 2009 letter and comments on the Quarterly Monitoring Report — Fourth <br /> Quarter 2oo8(Report) dated January 15, 2009 for the CCT Stockton Railyard,located at <br /> 1645 Cherokee Road in Stockton,California. <br /> Regarding the issues surrounding wells MW-5 and MW-6,the three current monitoring <br /> wells, MW-5,MW-6 and MW-7 were installed to depths of approximately 67 feet below <br /> grade(fbg)and the current depth to groundwater in those wells is approximately 53 fbg• <br /> Although a sufficient column of water is present in each well to obtain groundwater <br /> samples,well MW-5 has consistently been very slow to recover following purging and <br /> MW-6 was slow to recover during the fourth quarter monitoring event. <br /> A review of the boring logs and well construction details shows wells MW-5 and MW-6 <br /> are screened primarily within low permeability soils. With the exception of a thin sand <br /> lense near the base of the well screen intervals in each well,the primary soil type present <br /> over the screened interval in wells MW-5 and MW-6 is dense silt. Furthermore,well <br /> MW-5 was installed within the boundary of the excavation and the upper portion of the <br /> well screen interval is within the compacted fill material used to backfill the excavation. <br /> Based on the low permeability soils within the screened interval for wells MW-5 and MW- <br /> 6,it is not surprising that these wells do not readily recover following purging. <br /> Although the Site wells produced sufficient water during initial development and <br /> sampling back in June 2oo8 water levels at the Site have dropped significantly since June <br /> 20o8 and until recently there has been little to no precipitation and recharge. <br />